Description

These functions provide portable access to the members of the stdio(3C)FILE
structure.

The __fbufsize() function returns in bytes the size of the buffer currently
in use by the given stream.

The __flbf() function returns non-zero if the stream is line-buffered.

The __fpending function returns in bytes the amount of output pending on
a stream.

The __fpurge() function discards any pending buffered I/O on the stream.

The __freadable() function returns non-zero if it is possible to read from
a stream.

The __freading() function returns non-zero if the file is open readonly, or
if the last operation on the stream was a read operation such
as fread(3C) or fgetc(3C). Otherwise it returns 0.

The __fsetlocking() function allows the type of locking performed by stdio on
a given stream to be controlled by the programmer.

If type is FSETLOCKING_INTERNAL, stdio performs implicit locking around every operation on
the given stream. This is the default system behavior on that
stream.

If type is FSETLOCKING_BYCALLER, stdio assumes that the caller is responsible for
maintaining the integrity of the stream in the face of access by
multiple threads. If there is only one thread accessing the stream,
nothing further needs to be done. If multiple threads are accessing the
stream, then the caller can use the flockfile(), funlockfile(), and ftrylockfile() functions
described on the flockfile(3C) manual page to provide the appropriate locking. In
both this and the case where type is FSETLOCKING_INTERNAL, __fsetlocking() returns the
previous state of the stream.

If type is FSETLOCKING_QUERY, __fsetlocking() returns the current state of the stream
without changing it.

The __fwritable() function returns non-zero if it is possible to write on
a stream.

The __fwriting() function returns non-zero if the file is open write-only or
append-only, or if the last operation on the stream was a write
operation such as fwrite(3C) or fputc(3C). Otherwise it returns 0.

The _flushlbf() function flushes all line-buffered files. It is used when
reading from a line-buffered file.

Usage

Although the contents of the stdio FILE structure have always been private to
the stdio implementation, some applications have needed to obtain information about a
stdio stream that was not accessible through a supported interface. These applications have
resorted to accessing fields of the FILE structure directly, rendering them possibly
non-portable to new implementations of stdio, or more likely, preventing enhancements to
stdio that would cause those applications to break.

In the 64-bit environment, the FILE structure is opaque. The functions
described here are provided as a means of obtaining the information that
up to now has been retrieved directly from the FILE structure.
Because they are based on the needs of existing applications (such as mh
and emacs), they may be extended as other programs are ported.
Although they may still be non-portable to other operating systems, they will
be compatible from each Solaris release to the next. Interfaces that are
more portable are under development.